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I have an offgrid inverter/charger - an MPPSolar PIP4048MS (4000W inverter, 48V system). By and large it has worked well for 7 years.

Recently I bought an MPPSolar PIP5048MS (5000W inverter, 48V system) as a replacement. However, it keeps on tripping the RCD in the distribution panel. (The radial circuits for the lights work fine, there is no problem).

This RCD controls 7 MCB circuits. Each MCB circuit is a ring circuit with maybe 7 or 8 sockets (outlets) on it.

When I connect up the inverter and turn it on (in battery mode, with no ac input connection), I then go to the distribution panel and turn on each MCB at a time in order not to overload the inverter. This is when the problem begins.

If there is no load on the MCB circuit the MCB lifts and the RCD remains 'up'. However, if there is a load on the circuit - such as a 'fridge, freezer, etc. the RCD trips. On one particular circuit there is a small pump that controls a reverse osmosis system. The pump only needs to be in standby (not actively running) to cause the RCD to trip. I have tried a variety of loads - toaster, 100W coffee grinder, electric drill. As soon as the load is applied the RCD trips. The only thing (that I have tried) that doesn't cause a trip is a small table lamp.

In both models of the inverter there is a neutral-ground bond in the inverter while the inverter is in battery mode - this is the only mode that I have tried the new inverter in.

Because of the time involved in exchanging the 2 inverters and vica versa (in order to test the PIP5048) I decided to set up a small replica of the distribution panel out in the shed. The same result - the RCD trips in the same circumstances as above.

At the behest of the MPPSolar support I removed the screw inside the inverter responsible for the neutral-ground bond. It made no difference. As a result they say that the problem isn't caused by earth leakage from inverter. The earth leakage must be coming from the loads. However, I put the following to them:

In the meanwhile can you answer this one question please? If there is leakage current coming from the laptop or 'fridge or toaster, etc., etc. then why doesn't the RCD drop right now when any one of these appliances is used (now that I am using the 'old' PIP4048 or if I use the EPEVER). Why does the RCD wait to trip until the PIP5048 is used?

They haven't answered the question - they just keep repeating that I need to measure the leakage coming from the loads. (By the way, I did use a 5kW EPEVER inverter/charger for a few weeks at the start of summer with no RCD trips). The RCD is a 63A 30mA DP type A RCD.

Where do I go from here?

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  • \$\begingroup\$ In my experience conducted EMI from inverters can trip an RCD even though the leakage currents are not high enough to otherwise cause it to trip. I solved the problem with an isolation transformer, but for 5 kW inverter that would be a relatively large solution. You could maybe try an EMI filter. \$\endgroup\$
    – John D
    Oct 23, 2022 at 18:21
  • \$\begingroup\$ Thanks for that John D. I am wary of trying different things when the fault could be with the inverter itself (that it should be returned and replaced). Support at MPPSolar are saying that it is very rare and they don't know the cause. \$\endgroup\$ Oct 27, 2022 at 8:37
  • \$\begingroup\$ Fair point, I kind of meant after measuring and verifying that the leakage current isn't the issue. \$\endgroup\$
    – John D
    Oct 27, 2022 at 14:17

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The type of RCD being used might be the problem, I might of come across something similar with inverters on a machine before.

We have a machine in work which has 6 inverters each driving 7 diffrent motors (one inverter dives 2 motors), each of these have its own MCB inside the machine but all share same RCD. No matter what order I put them MCB's on the last one always causes the RCD to trip. Even if I only have half of the inverters on it causes the inverters to do some crazy stuff, randomly causes motors to stop and start when ever they like and fault codes to appearing on the inverters. Removed RCD and the machine works perfectly, all inverters and motors work as they should, no random stopping and starting and no error codes!

I have read it could be to do with electrical noise and harmonic distortion caused by the inverters that make the RCD trip.

I have also been looking into types of RCDs and maybe a type F or type B would be better for your situation.

Type F and type B RCD does what a type A and type AC RCD does and more. But I think they can handle the harmonic distortion better caused by the inverters :D

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  • \$\begingroup\$ Thanks for that. I need to correct something in my original post/question. I found an error in the circuit that I set up in my shed. Having sorted out the problem I find that the RCD does not trip in this simple circuit (just one outlet). When I plug in a 'fridge or a drill, etc. the RCD does not trip. Back in the house the problem still remains, however. I isolated one of the ring circuits and connected the PIP5048 to this circuit alone. RCD trips. So, a simple circuit, with just one outlet, works okay out in the shed. However, one ring circuit, with perhaps 9 outlets on it (with 3 of them \$\endgroup\$ Apr 9, 2023 at 13:40
  • \$\begingroup\$ in use) causes the RCD to trip. This seems very strange to me. \$\endgroup\$ Apr 9, 2023 at 13:43
  • \$\begingroup\$ I did consider a type B RCD. They are not normally stocked in electrical stores. They can be got but are expensive. For that reason I have not purchased one. I would need to be more sure that it would solve the problem. \$\endgroup\$ Apr 9, 2023 at 13:48
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the issue you're encountering stems from the fact that the current you're measuring through the Residual Current Device (RCD) includes both steady-state and switching currents. Since the RCDs may have limited bandwidth, there can be a phase shift between these currents (positive and negative), preventing them from canceling each other out. Instead, they add up, leading to false trips.

To address this, you should first analyze the harmonic order of the currents. Then, install an RC filter at the output terminal of the RCD, before the trip command generating circuit. This filter will effectively reduce the switching frequency harmonics, mitigating the false trip problem.

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  • \$\begingroup\$ Thank you for your answer Archit6586. What you write makes sense. As regards analyzing the harmonic order of the currents how best should I do this? Do I need to do this to determine the type of RC filter needed?An earlier contributor suggested using a different type of RCD, such as Type B or F. Have you view on this? \$\endgroup\$ Apr 17 at 19:22

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